The invention concerns, first, a length of hose made out of an elastic material that readily recovers its shape, especially intended for covering the coiled section of a helical compression spring with a progressive characteristic of the type employed in motor vehicles and similar machines, and, second, a method of manufacturing it.
Helical compression springs are employed in the suspensions of motor vehicles. If the spring has a progressive characteristic, at least one section of the rod that it is made out of tapers conically near the end through at least one winding, with the very end of the rod becoming cylindrical again, although with a shorter cross-section. The tapered section near the end of a helical compression spring of this type is enclosed in an extruded hose of constant cross-section to reduce noise and to protect the spring against corrosion. A length of hose of this type is made out of an elastic and readily recovering plastic, thermoplastic polyurethane for example, and has a large enough cross-section or inside diameter to allow it to be drawn loosely over the tapered section, with its initial section resting tight against the larger or regular cross-section of the spring rod due to the elasticity of the plastic and secured at that point. The other end of the hose-like cover is closed. Before a length of hose of this type can be drawn over the spring, a liquid anticorrosion agent and lubricant is injected into the hose to facilitate drawing it over the spring and to extensively prevent corrosion of the tapered section of the spring surrounded by the hose. Aside from the necessity of the additional operation of closing off one end of the hose, the welded-together end of a length of hose of this type, which is relatively loose in the vicinity of the reduced spring-rod cross-section is likely to become damaged as the result of outside events and allow the liquid it contains to leak out and admit moisture, dirt, etc. It is in particular the desirable protection against corrosion that is accordingly lost.